Charles Adams, who is single, retired on March 3, 2019, at the age of 65. For the year 2019, he receives the following income:

Salary $14,000
Interest income 2,000
Dividend income 2,000
Tax-exempt income 1,000
Social Security benefits 5,000
Net rental income 6,000

What is Charles' modified AGI? What amount, if any, of his Social Security benefits must Charles include in his 2019 gross income? What is Charles' taxable income for 2019?